Pre-insulated connector and method of making the same



Se t. 10, 1957 E. w. FORNEY, JR

PRE-INSULATED CONNECTOR AND METHOD OF MAKING THE SAME Filed April 7, 1953 I [I'll/Illa United States Patent '0 Edgar W. Forney, Jr., Dauphin, Pa., assignor to AMP Incorporated Application April 7, 1953, Serial No. 347,413

2 Claims. (Cl. 339-276) This invention relates to solderless connectors of the type that are adapted to 'be crimped on the ends of electrical conductors either to provide a terminal on the condoctor .or to connect two conductors together. More particularly the invention relates to a novel method of making an improved pre-insulated connector and to the pre-insulated connector thus produced. .Solderless connectors of the type to which the present invention relates commonly comprise a barrel or ferrule made of a relatively soft metal such as pure copper and an insulating sleeve made of a tough plastic surrounding the barrel. The stripped end of an electrical conductor that is to be terminated or connected to another conductor is inserted in the barrel of the connector and pressure is exerted on the exterior surface of the insulating sleeve by a suitable crimping tool to force the metal of the barrel against the conductor end to make a physically strong and electrically efficient connection therebetween.

Typical connectors to which the present invention is applicable are shown in Watts Patent 2,410,321 and Broske Patent 2,478,082. The former patent shows a terminal adapted to be used in terminating a conductor and the latter patent discloses a so-called straight-through or butt connector adapted to be used in connecting two conductors together in .end-to-end relationship. In both cases the connector includes a metal barrel or ferrule surrounded by a plastic insulating sleeve. As the description proceeds, it will become apparent that the present invention is applicable not only to these two types of connectors but also to other connectors comprising a metal barrel or ferrule-forming portion and an insulating sleeve.

While the insulating sleeve may be made of any of various plastics, it has been found that for many applications it is advantageous to use a sleeve made of nylon. For example, the use of nylon for the insulating sleeve is. particularly desirable in those cases where the connector may be exposed to liquids having a high solvent power such as certain of the liquids used in hydraulic brake systems. However, it has also been found that nylon has a tendency to extrude when subjected to the pressure of the crimping tool, and thus when nylon insulation is used there is a tendency for the nylon to squeeze out axially or circumferentially or both to such an extent that the resulting insulation thickness at the crimped area may be insuflicient to provide the desired dielectric strength. I

It is accordingly an object of the present invention to provide an improved pre-insul'ated connector. -It is another =object of the invention to provide a pre-insulated connector wherein the tendency of the plastic insulation to extrude during crimping is materially reduced. It is still another object of the invention to provide a novel method of making such a connector. Other objects of the invention will be in part obvious and in part pointed out hereafter.

' t In one of its broader aspects the present invention comprises a method of producing a connector that involves treating at least the external surfaces of a metal barrel or ferrule-forming portion thereof to produce thereon a rough texture similar to that of sandpaper. This sandpaper finish cooperates with the interior surface of a subsequently applied plastic sleeve to inhibit axial and circumferential movement of the sleeve material with respect to the metal barrel of the connector. Thus when crimping pressure is subsequently applied to the connector slippage of' the interior surface of the plastic sleeve with respect to the barrel of the connector is prevented and hence axial extrusion of the material of the sleeve is retarded. As described below, the use of a roughened surface on the connector barrel can advantageously be supplemented by treating the insulating sleeve with a material capa-ble of increasing the coefiicient of friction between the exterior of the sleeve and the crimping tool, if desired.

The many objects and advantages of the present invention can best be understood and appreciated by reference to the accompanying drawing wherein:

Fig. 1 is an exploded perspective view of a terminal and plastic insulating sleeve therefor, particularly showing the roughened surface of the barrel of the terminal;

Fig. 2 is an axial section through the assembled terminal and insulating sleeve showing the assembled relation of the roughened surface of the barrel and the insulating sleeve;

Fig. 3 is a perspective view of the insulated terminal after ,it has been crimped on the end of an electrical conductor;

Fig. 4 is an exploded perspective view of a solderless connector of the type that is adapted to be crirnped to the ends of two electrical conductors to interconnect them; and

Fig. 5 is an axial section through the connector of Fig. 4 and showing the parts in assembled relation.

Referring to the drawing :and more particularly to Fig. 1, the terminal there shown comprises a tongue portion 10 and 'barrel portion 12 having thereon a layer 14 of gritty material that is prepared and applied in a manner described in further detail hereafter. The terminal also comprises a plastic insulating sleeve 16 which may be made for example of nylon, and fits snugly over the barrel portion 12 of the terminal. The assembled relation of the parts is shown in Fig. 2 of the drawing.

In use the uninsulated end of an insulated conductor is inserted in the barrel 12 of the terminal and crimping pressure is applied to the exterior of the sleeve 16 to force the barrel 12 against the end of the conductor and thereby'm'ake an effective electrical connection between the terminal and conductor. The appearance of the terminal after it has been applied to the conductor is illustrated in Fig. 3 of the drawing.

Referring now to Fig. 4 of the drawing, a different type of solderless connector is there shown which is of the general type shown in Broske 2,478,082 and comprises a metal tube 18 having a central cut out portion or recess 20. The connector also comprises a pair of sleeves 22 and 24 that fit over the ends of the tube 1'8. The sleeves 22 and 24 are provided with layers 26 and 28 of a gritty material that is prepared and applied in a manner described in detail hereafter. In general the gritty layers 26 and 2'8 are applied by dipping the sleeves 22 and 24 in a suspension of the gritty material and hence the sleeves are both internally and externally coated with the gritty material.

As shown in Figs. 4 and 5 the connector further comprises a plastic insulating sleeve 30 which when the parts are in assembled relation, covers both the tube 18'and the sleeves 22 and 24. The gritty layers 26 and 28 cooperate with the interior surface of plastic sleeve, 30 to 3 I prevent extrusion of plastic sleeve material when the connector is crimped. The sleeve 30 is preferably made of a transparent or translucent plastic so that the portion 32 of the sleeve 30 in the registry with the recess 20 of tube 18 forms a window through which it is possible to view the abutting ends of conductors that are inserted into the tube 18 for crimping.

In this way proper positioning of the conductors within tube 18 is insured.

The roughened surface on the metal barrel 12 'of the connector can be conveniently produced by forming thereon a resin layer 14 containing a finely divided gritty material. The finely divided gritty substance is dispersed in a solvent solution of the resin and the resulting suspension is applied to the connector barrel by spraying, brushing or the like. The solvent is then caused to evaporate to deposit the plastic layer containing the gritty material. Thereafter the plastic insulating sleeve 16 is slipped over the treated connector barrel. The inner diameter of the sleeve is made ofsuch size that the sleeve fits snugly on the connector barrel and hence when crimping pressure is applied the roughened surface of the connector barrel prevents axial and circumferential inovement of the adjacent surface of the insulating sleeve. In some cases part of the connector assembly is comprised of a seamless metal tube which is placed over the barrel portion of the connector to support and cover a joint resulting from the formation of the barrel from flat stock. The use of such a seamless metal tube is illustrated in Swengel Patent 2,654,873. In these cases the solution can be applied most efficiently by dip-coating the metal tube. Similarly the gritty layers 26 and 28 of the connector shown in Figs. 4 and 5 of the drawing are prefera'bly applied by dip-coating the sleeves 22 and 24 in the solution.

In cases where the sleeve is made of nylon it has been found advantageous to pre-treat the nylon sleeve to form a coating of a vinyl resin thereon. This can conveniently be done by preparing an organic solvent solution of the vinyl resin, dipping the nylon sleeve therein and evaporating the solvent to deposit a very thin coating of the vinyl resin on the nylon sleeve. Alternatively the vinyl resin coating can be applied to the nylon sleeve after it has been assembled with the connector. It has been found that such a vinyl resin coating on the nylon sleeve increases the coefficient of frictionbetween the exterior of the sleeve and the crimping tool thereby further inhibiting axial extrusion of the nylon during crimping. .Also the vinyl resin coating on the sleeve improves the surface finish of the sleeve, and cooperates effectively with the roughened layer of the connector barrel to decrease further the tendency of the nylon sleeve to extrude under crimping pressure.

It has been further found that nylon insulating sleeves tend to absorb undesired moisture from the atmosphere and that this moisture can be conveniently removed by baking the sleeves under suitable conditions e. gheating' to a temperature of 180 F. for one hour. resin coating step described above can be conveniently applied to the insulating sleeves after such a heat treatment to prevent re-absorption of moisture, at least until the connectors are crlmped. -'It is evident that the vinyl resin coating can be applied to the nylon sleeve after it has been assembled on the connector as well as before assembly, and it is advantageously applied after assembly in cases where the nylon sleeve has been heat treated, because of the fact that the abrasive layer on the conand presented for purposes of illustration in order to make clear the principles of the invention and the practical employment of those principles in applying the invention to practical use and thus so fully to instruct others skilled in the art that they will be enabled readily to modify and to select substitutes and alternatives each as may be best suited to the particular conditions of any given application or use. 7

One part by weight of a vinyl resin manufactured by the Bakelite Corporation and identified by the manufacturer as VMCH is dissolved in five parts by weight of methyl-isobutyl ketone. The resulting solution is divided into two parts which for convenience will be designated as solution A and solution B. A finely ground pumice stone is then added to solution A in the ratio of 1 part by weight of the finely divided solid to 5 parts of solution and the pumice stone is held in suspension by continuous agitation. The finely ground pumice stone or grit is of such size that 87.5% passes through a 200 mesh screen and an additional 11.4% has a particle size between 1'00 and 200 mesh. Thus substantially all of the material in suspension has a particle size less than 100 mesh.

Sleeves such as the sleeves 2-2 and 24 or barrel support tubes of the type referred'to above are dip-coated in solution A and the solvent is evaporated to produce on the tube and particularly on its exterior surface a vinyl resin layer or coating containing the pumice grit. Thus the exterior surface of the connector assembly has a sandpaper finish.

A nylon sleeve of such size as to fit snugly over the connector barrel tube and made of nylon manufactured by E. I. du Pont de Nemours Company and designated by the manufacturer as FM3003 is then dip-coated in solution B and air dried to remove the solvent therefrom and deposit a thin coating of the vinyl resin thereon. The coated nylon sleeve is then assembled over the coated metal tube of the connector barrel and the resulting assembly baked in an air oven for twenty minutes at 180 F. This heating step aids in removing the remaining solvent from the vinyl film and in addition facilitates some 'diametrical shrinkage of the nylon thus bringing it into more intimate contact with the roughened surface of the connector barrel.

It has been found that pre-insulated connectors made according to the above-described process can be crimped at substantially higher pressures than untreated connectors without excessively thinning out the insulating layer during crimping.

It is of course to be understood that the specific exam ple given above is illustrative only and that various modifications can be made within the scope of the invention.

Thus the connector barrel or a metal tube positioned The vinyl nector has a tendency to scrape the coating during assem bly of sleeve and connector.

In order to point out more fully the nature of the present invention, I will describe below an illustrative method of preparing and applying the gritty layer to the connector. However, it should be understood that this illustrative method is not intended to be exhaustive or limitingof the invention but on the contrary is chosen thereon can be coated with other types of resins than the vinyl resins specifically referred to, and finely divided gritty niaterial other than pumice can be used to provide the roughened surface. It will be appreciated that the action of the pumice is primarily mechanical, or physical, in character and therefore that satisfactory results may be achieved in the absence of any gritty material where the metal barrel carries a plating presenting a rough surface or for some other reason is not objectionably smooth. Pre-treatrnent of the plastic sleeve is not essential in every circumstance and is unnecessary where, for example, the insulating sleeve is made of a vinyl resin rather than nylon. In the appended claims the phrase conductor-receiving barrel is intended to comprehend the barrel portion of the connector either with or Without anieta-l tube positioned thereon as described above. Other modifications within the scope of the invention will be apparent to those skilled in the art.

What is claimed as new is:

L An insulated electrical connector adapted to be erunped onto an electrical conductor, comprising a metal ferrule adapted to receive the conductor, a nylon insulating sleevehaving a moisture content Within a range that will maintain the nylon in tough, pliable, condition, and means for maintaining the moisture content range including a film of vinyl resin covering the entire surface of the nylon whereby transference of moisture between the nylon and the atmosphere is prevented.

2. The device of claim 1 including gritty particles between the metal ferrule and the nylon sleeve to increase the coeflicient of sliding friction therebetween.

References Cited in the file of this patent UNITED STATES PATENTS Moolre Oct. 13, 1931 Brenizer Apr. 28, 1936 Bergan Nov. 18, 1952 Swengel Oct. 6, 1953 Wooley Aug. 16, 1955 

